The present invention relates to a support member for photographic printing paper to give excellent image, and in particular to a support member for photographic printing paper to increase whiteness degree and to provide excellent sharpness.
In recent years, a support member for waterproof photographic printing paper has been used, both sides of which are coated with polyolefin such as polyethylene for rapid development processing of photographic printing paper. However, photographic image obtained from the photographic printing paper using polyolefin-coated paper is disadvantageous in that resolving power is not very high.
The reason for this may be as follows: In a polyolefin-covered support member, white pigment is mixed in polyolefin layer of the surface which contacts photosensitive silver halide emulsion, while the quantity of white pigment thus mixed is so small and shielding effect is not sufficient that light scatters within the polyolefin layer.
Normally, titanium oxide is used as the white pigment. Improvements of surface coating of titanium oxide to increase the quantity filled into polyolefin have been disclosed in Japanese Patent Laid-Open Publication No. 55-108658 and Japanese Patent Laid-Open Publication No. 57-35855, etc., and simultaneous use with other pigment is disclosed in Japanese Patent Publication No. 49-27046. In any case, however, filling quantity of titanium oxide is up to 15 weight % at the highest.
In this respect, methods are described in Japanese Patent Publication No. 57-53937 and Japanese Patent Laid-Open Publication No. 57-64235, by which a white pigment layer comprising white pigment and hydrophilic colloid solution is placed on a film or a resin-coated paper, and a photosensitive emulsion layer is placed on the white pigment layer. In the photographic printing paper using the support member disclosed in these patents, binder of the white pigment layer is hydrophilic and absorbs development processing solution or water, and it is disadvantageous because drying is delayed compared with the photographic printing paper using ordinary polyolefin-coated paper as the support member.
A method to coat an aqueous emulsion comprising binding agent and pigment is disclosed in Japanese Patent Laid-Open Publication No. 50-44818. However, when aqueous material is coated, drying is delayed and high-speed processing is not achievable, or drying zone must be extremely enlarged. Further, when emulsion is used, mechanical stability of the emulsion is reduced and uniform coating is not accomplished when gravure roll or bar are coated continuously.
To overcome the above problems, Japanese Patent Laid-Open Publication No. 59-200234 discloses a method, by which a binder soluble in organic solvent and white pigment are coated. By these methods, it is possible to increase filling ratio of white pigment in the binder, to raise masking power of the pigment layer of the support member, and to increase sharpness of photographic image. Masking power of pigment layer exerts strong influence on sharpness of photographic image and it is determined almost completely by white pigment. Thus, there is a limit in the sharpness of the photographic image obtained.
It is an object of the present invention to provide a support member for photographic printing paper to increase whiteness degree and to give photographic image with higher sharpness.